Minor issue in lwipopts.h in macro expansion in parameters (cosmetic
change: it expands correctly but doesn't pass the expected argument)
Fix lwip thread safety issue in tests: dhcp server should be started and
stopped only in lwip context/thread. Without this fix, the test would
fail if `CONFIG_LWIP_CHECK_THREAD_SAFETY=y`
Adds CONFIG_LWIP_TCPIP_CORE_LOCKING=y to some mqtt example tests (the
same configs as used in v5.1)
Testing with predefined buffer sizes for MQTT as well as mbedTLS to
exercise fragmenting outgoing data on both layers. Example test compares
received partition with the actual binary file.
